Taut-MUSHRA: A MUSHRA-based method without hidden reference and anchors for relative sound quality evaluation

State-of-the-art text-to-speech systems have improved in sound quality and have become increasingly large in terms of the number of subjects to detect differences in MOS evaluation, which uses the five-scale precision. The MUSHRA method can precisely detect differences in sound quality compared with the MOS method because sound qualities are rated on a relative scale of 0 to 100 on 101 scales. However, it has the drawback of requiring hidden reference and anchors; thus, it cannot detect cases exceeding the hidden reference. Our method, named Taut-MUSHRA, requires no hidden reference and anchors and instead adds two constraints to the subjects. As a result, compared with the MOS method, our Taut-MUSHRA method could more sensitively detect differences in sound quality.